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United States Patent |
5,545,449
|
Tiedeman
|
August 13, 1996
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Polyether-reinforced fiber-based materials
Abstract
Polyether-reinforced fiber-based materials, and methods for their
manufacture, are disclosed. A representative material is a sheetlike ply
having on one or both faces thereof a polyether-impregnated stratum
extending depthwise into the ply thickness dimension no greater than about
one-half the ply thickness dimension so as to leave a portion of the ply
thickness dimension unimpregnated with polyether. The materials can
comprise plural superposed plies wherein at least one ply has at least one
polyether-impregnated stratum, such as polyether-reinforced corrugated
paperboard. The polyether-reinforced materials have excellent compression
strength and foldability. Each polyether-reinforced stratum is made by
controllably applying a low-viscosity liquid mixture of an epoxy resin and
a hardener, wherein the epoxy resin is substantially non-prepolymerized,
to a fibrous web surface, then curing the resin mixture. The
polyether-reinforced materials can be folded after curing and are useful
for making cartons and other products.
Inventors:
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Tiedeman; George T. (Seattle, WA)
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Assignee:
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Weyerhaeuser Company (Tacoma, WA)
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Appl. No.:
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850980 |
Filed:
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March 12, 1992 |
Current U.S. Class: |
428/34.2; 162/164.3; 162/168.6; 428/36.1; 428/36.2; 428/182; 428/413; 428/414; 428/534; 428/535; 442/381 |
Intern'l Class: |
D21H 017/52; B32B 027/10; B32B 029/08 |
Field of Search: |
162/164.1,164.3,168.1,168.6
;286
428/34.2,413,414,534,535,536,537.5,411.1,36.1,36.2,290,175,182,260,262,269,274
264/257,258
|
References Cited
U.S. Patent Documents
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|
3451957 | Jun., 1969 | Pritchard | 106/245.
|
3462383 | Aug., 1969 | Longoria, III | 162/164.
|
3584072 | Jun., 1971 | Winslow | 162/164.
|
3607598 | Sep., 1971 | LeBlanc et al. | 428/182.
|
3616163 | Oct., 1971 | Reisman | 428/182.
|
3617427 | Nov., 1971 | LeBlanc | 428/182.
|
3617428 | Nov., 1971 | Carlson | 428/182.
|
3617429 | Nov., 1971 | LeBlanc | 428/182.
|
3619341 | Nov., 1971 | Elmer | 428/182.
|
3619342 | Nov., 1971 | Burke | 428/182.
|
3630834 | Dec., 1971 | Bremmer | 162/164.
|
3666593 | May., 1972 | Lee | 156/285.
|
3673558 | Jun., 1972 | Toepel et al. | 162/164.
|
3682762 | Aug., 1972 | LeBlanc | 428/182.
|
3687767 | Aug., 1972 | Reisman et al. | 156/210.
|
3697365 | Oct., 1972 | Reisman et al. | 428/182.
|
3886019 | May., 1975 | Wilkinson et al. | 156/210.
|
3915783 | Oct., 1975 | Goppel et al. | 428/413.
|
4046935 | Sep., 1977 | Wilkinson et al. | 428/182.
|
4051277 | Sep., 1977 | Wilkinson et al. | 427/288.
|
4056510 | Nov., 1977 | Symm et al. | 162/164.
|
4091167 | May., 1978 | Okada et al. | 428/413.
|
4096305 | Jun., 1978 | Wilkinson et al. | 428/182.
|
4397909 | Aug., 1983 | Goddard et al. | 428/262.
|
4582735 | Apr., 1986 | Smith | 428/34.
|
4654100 | Mar., 1987 | Yats et al. | 162/164.
|
4656094 | Apr., 1987 | Kojima et al. | 428/262.
|
4673616 | Jun., 1987 | Goodwin | 428/290.
|
4740407 | Apr., 1988 | Schaefer et al. | 428/290.
|
4980234 | Dec., 1990 | Almer et al. | 428/414.
|
5008359 | Apr., 1991 | Hunter | 527/103.
|
5258087 | Nov., 1993 | Symons | 428/182.
|
5292391 | Mar., 1994 | Wallick | 156/205.
|
Foreign Patent Documents |
2087423 | Dec., 1971 | FR.
| |
55-6557 | Jan., 1980 | JP.
| |
57-95397 | Jun., 1982 | JP.
| |
57-95447 | Jun., 1982 | JP.
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57-182436 | Nov., 1982 | JP.
| |
59-47497 | Mar., 1984 | JP.
| |
59-112096 | Jun., 1984 | JP.
| |
59-179896 | Oct., 1984 | JP.
| |
60-224537 | Nov., 1985 | JP.
| |
62-152735 | Jul., 1987 | JP.
| |
1287829 | Sep., 1972 | GB.
| |
1301132 | Dec., 1972 | GB.
| |
1408431 | Oct., 1975 | GB.
| |
WO92/09645 | Jun., 1992 | WO.
| |
Other References
TAPPI Test Method No. T 511 om-88, "Folding Endurance of Paper (MIT
Tester)." 1988.
TAPPI Test Method No. T 818 om-87, "Ring Crush of Paperboard."1987.
Specification, drawings, and claims as allowed for U.S. Patent Application
Serial No. 07/692,861, filed Apr. 29, 1991, (Inventor: Scott A. Wallick).
"Beef Up Corrugated Board to Hike Boxes Wet Strength,"Package Engineering,
pp. 56-57 (Dec., 1970).
Mithel, "Research in Low-Cost Polymer Reinforcing Proves Applications to
Corrugated," Paperboard Packaging, pp. 38-48 (Oct., 1973).
Hamerstrand et al., "Starch Xanthides in Linerboard: A Continuous Wet-End
Process,"TAPPI 50: 98A-100A (Aug., 1967).
Morak and Ward, "Cross-Linking of Linerboard to Reduce Stiffness Loss, II.
Diisocyanates in Liquid Phase Application," TAPPI 53: 652-656 (Apr.,
1970).
Morak and Ward, "Cross-Linking of Linerboard to Reduce Stiffness Loss, III.
Diisocyanates in Vapor-Phase Application," TAPPI 53: 1055-1058 (Jun.,
1970).
Morak et al., "Cross-Linking of Linerboard to Reduce Stiffness Loss, IV.
Application of Blocked Diisocyanates," TAPPI 53: 2278-2283 (Dec., 1970).
Gaul et al., "Novel Isocyanate Binder Systems for Composite Wood Panels,"
in Polyurethane: New Paths to Progress, Marketing, Technology, Proceedings
of the S.P.T. International Technical/Marketing Conference, San Diego, CA,
Nov. 2-4, 1983, pp. 389-407.
|
Primary Examiner: Robinson; Ellis P.
Assistant Examiner: Dye; Rena L.
Attorney, Agent or Firm: Klarquist Sparkman Campbell & Leigh
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
The present application is a continuation-in-part of co-pending U.S. patent
application Ser. No. 07/770,587, filed on Oct. 2, 1991, pending.
Claims
I claim:
1. A reinforced fibrous material, comprising a first fibrous sheet having
an obverse face, a reverse face parallel to the obverse face, a sheet
thickness dimension extending between the obverse and reverse faces, and a
polyether-impregnated stratum extending parallel to the obverse and
reverse faces and located within the sheet thickness dimension, the
stratum having a stratum thickness dimension controlled to be no greater
than about one-half the sheet thickness dimension such that a portion of
the sheet thickness dimension is unimpregnated with polyether so as to
confer an increased combination of ring crush strength and flexibility to
the fibrous material compared to an otherwise similar material lacking the
polyether-impregnated stratum, the polyether being formed by a
polymerization reactioD involving an epoxy resin comprising molecules
having a terminal glycidyl group and a hardening or curing agent, the
resin mixture having a viscosity of less than 500 centipoise and the first
fibrous sheet containing the polvether is formed into corrugated medium.
2. A material as recited in claim 1 wherein the fibers of the first fibrous
sheet are selected from a group consisting of woven and non-woven fibers.
3. A material as recited in claim 1 wherein the fibers of the first fibrous
sheet are selected from a group consisting of hydrophilic fibers,
hydrophobic fibers, and mixtures of hydrophobic and hydrophilic fibers.
4. A material as recited in claim 3 wherein the fibers of the first fibrous
sheet comprise wood-pulp fibers.
5. A material as recited in claim 4 wherein the first fibrous sheet is a
paperboard.
6. A material as recited in claim 5 wherein the polyether-impregnated
stratum comprises polyether at a loading level no greater than about 10%
w/w relative to the mass of the paperboard.
7. A material as recited in claim 6 wherein the paperboard has a basis
weight of about 42 pounds and the polyether-reinforced fibrous material
has a ring-crush strength greater than about 100 pounds at 50 percent
relative humidity when tested according to TAPPI T818-OM-87.
8. A material as recited in claim 7 having a foldability, when said
material is tested according to TAPPI T511-OM-83, substantially the same
as an untreated control paperboard having a basis weight of about 42
pounds.
9. A material as recited in claim 1 wherein the thickness dimension of the
polyether-impregnated stratum extends from the obverse face into the
thickness dimension of the sheet.
10. A material as recited in claim 1 wherein the first fibrous sheet
comprises a first polyether-impregnated stratum having a first-stratum
thickness dimension extending from the obverse face into the sheet
thickness dimension, and a second polyether-impregnated stratum having a
second-stratum thickness dimension extending from the reverse face into
the sheet thickness dimension the first- and second-stratum thickness
dimensions beinq controlled so as to provide an unimpregnated stratum
between the first and second polyether-impregnated strata.
11. A material as recited in claim 1 further comprising a second fibrous
sheet coextensive with the first fibrous sheet, wherein the second fibrous
sheet has an obverse face, a reverse face parallel to the obverse face,
and a thickness dimension extending between the obverse and reverse faces,
and wherein the obverse face of the first fibrous sheet is adhered to the
reverse face of the second fibrous sheet.
12. A material as recited in claim 11 wherein the second fibrous sheet has
a polyether-impregnated stratum of fibers extending parallel to the
obverse and reverse faces of the second fibrous sheet and located within
the thickness dimension of the second fibrous sheet, the
polyether-impregnated stratum having a stratum thickness dimension
controlled to be less than the thickness dimension of the second fibrous
sheet such that a portion of the thickness dimension of the second fibrous
sheet is unimpregnated with polyether.
13. A material as recited in claim 11 wherein the first fibrous sheet is a
medium paperboard and the second fibrous sheet is a linerboard.
14. A carton blank made from the material of claim 1.
15. A carton made from the material of claim 1.
16. A reinforced fibrous material. comprising a first fibrous sheet having
an obverse face, a reverse face parallel to the obverse face, a sheet
thickness dimension extending between the obverse and reverse faces, and a
polyether-impregnated stratum extending parallel to the obverse and
reverse faces and located within the sheet thickness dimension, the
stratum having a stratum thickness dimension controlled to be no greater
than about one-half the sheet thickness dimension such that a portion of
the sheet thickness dimension is unimpregnated with polyether so as to
confer an increased combination of ring crush strength and flexibility to
the fibrous material compared to an otherwise similar material lacking the
polyether-impregnated stratum, the polyether being formed by a
polymerization reaction involving an epoxy resin comprising molecules
having a terminal glycidyl group and a hardening or curing agent, the
resin mixture having a viscosity of less than 500 centipoise and the first
fibrous sheet containing the polyether is formed into corrugated medium;
wherein the first fibrous sheet comprises a first polyether-impregnated
stratum having a first-stratum thickness dimension extending from the
obverse face into the sheet thickness dimension, and a second
polyether-impregnated stratum having a second-stratum thickness dimension
extending from the reverse face into the sheet thickness dimension the
first- and second-stratum thickness dimensions being controlled so as to
provide an unimpregnated stratum between the first and second
polyether-impregnated strata; and
wherein the first- and second-stratum thickness dimensions are each
controlled to be no greater than about one-third the sheet thickness
dimension.
17. A reinforced fibrous material, comprising a first fibrous sheet having
an obverse face, a reverse face parallel to the obverse face, a sheet
thickness dimension extending between the obverse and reverse faces, and a
polyether-impregnated stratum extending parallel to the obverse and
reverse faces and located within the sheet thickness dimension, the
stratum having a stratum thickness dimension controlled to be no greater
than about one-half the sheet thickness dimension such that a oortion of
the sheet thickness dimension is impregnated with polyether so as to
confer an increased combination of ring crush strength and flexibility to
the fibrous material compared to an otherwise similar material lacking the
polyether-impregnated stratum, the polyether being formed by a
polymerization reaction involving an epoxy resin comprising molecules
having a terminal glycidyl group and a hardening or curing agent, the
resin mixture having a viscosity of less than 500 centipoise;
the material further comprising a second fibrous sheet coextensive with the
first fibrous sheet, wherein the second fibrous sheet has an obverse face,
a reverse face parallel to the obverse face, and a thickness dimension
extending between the obverse and reverse faces, and wherein the obverse
face of the first fibrous sheet is adhered to the reverse face of the
second fibrous sheet; and
the material further comprising a third fibrous sheet coextensive with and
adhered to the reverse face of the first fibrous sheet, wherein the third
fibrous sheet is a linerboard, and wherein the first fibrous sheet is a
corrugated medium paperboard including a first polyether-immreqDated
stratum having a first-stratum thickness dimension extendinq from the
obverse face into the sheet thickness dimension, and a second
polyether-impregnated stratum having a second-stratum thickness dimension
extending from the reverse face into the sheet thickness dimension the
first and second-stratum thickness dimensions being controlled. so as to
provide an unimpregnated stratum between the first and second
polyether-impregnated strata.
18. A reinforced paperboard comprising:
a first paperboard ply having an obverse face, a reverse face parallel to
the obverse face, and a ply thickness dimension extending between the
obverse and reverse faces; and
a second paperboard ply coextensive with and adhered to the first
paperboard ply, the second paperboard ply having an obverse face, a
reverse face parallel to the obverse face, and a ply thickness dimension
extending between the obverse and reverse faces, wherein at least the
second one of said paperboard plies has on at least one of the obverse and
reverse faces thereof a polyether-impregnated stratum coextensive with the
corresponding face and having a stratum thickness dimension extending
depthwise from the corresponding face into the corresponding ply thickness
dimension, the stratum thickness dimension being controlled to be no
greater than about one-half the corresponding ply thickness dimension,
wherein a portion of the Corresponding ply thickness dimension is
unimpregnated with polyether so as to confer an increased combination of
ring crush strength and flexibility to the paperboard compared to an
otherwise similar material lacking the polyether-impregnated stratum, the
polyether being formed by a polymerization reaction involving an epoxy
resin and a curing agent, the epoxy resin comprising molecules each having
a terminal glycidyl group, the resin mixture having a viscosity of less
than 500 centipoise;
the reinforced paperboard further comprising a third paperboard ply
coextensive with and adhered to the second paperboard ply; and
wherein the first and third paperboard plies are linerboards and the second
paperboard ply is a corrugated medium paperboard interposed between the
first and third paperboard plies.
19. A reinforced paperboard as recited in claim 18 wherein each of said
first and second plies has on at least one of said obverse and reverse
faces thereof a polyether-impregnated stratum coextensive with the
corresponding face and having a stratum thickness dimension extending
depthwise from the corresponding face into the corresponding ply thickness
dimension, each stratum thickness dimension beinq controlled to be no
greater than about one-half the corresponding ply thickness dimension,
wherein a portion of the corresponding ply thickness dimension is
unimpregnated with polyether.
20. A reinforced paperboard as recited in claim 19 wherein the first ply is
a linerboard and the second ply is a medium paperboard.
21. A reinforced paperboard as recited in claim 20 wherein the medium
paperboard is corrugated.
22. A carton blank made from the material of claim 18.
23. A carton made from the material of claim 18.
Description
FIELD OF THE INVENTION
The present invention relates to reinforced fiber-based materials such as
reinforced fiberboards and reinforced paperboards, and containers made
therefrom.
BACKGROUND OF THE INVENTION
Fiberboards, including corrugated and noncorrugated paperboards, are useful
for an extremely wide variety of applications, but particularly for making
containers such as packaging and shipping containers. Modern techniques
for making such containers involve not only manufacturing the requisite
fiberboard material but also cutting and shaping of one or more sheets of
the fiberboard into "box blanks" that are folded into the corresponding
container shape. Box blanks are typically designed with multiple scored
lines and the like so that the blank can be readily formed into a
container by merely folding the box blank in an ordered manner along the
scored lines. Regardless of the container design, the forming of a
substantially planar box blank into a corresponding three-dimensional
container involves subjecting the fiberboard to a plurality of folds.
One drawback to many fiberboards, including paperboard, is their poor
rigidity when wet. To overcome this shortcoming, manufacturers have tried
various ways of reinforcing fiberboard and rendering the fiberboard
nonabsorptive for liquids. Examples of such reinforcement include
impregnating or coating the fiberboard with paraffin or other polymeric
material.
Paraffin coating substantially decreases the tendency of the fiberboard to
absorb water, making paraffin-reinforced corrugated paperboard popular for
use in packaging vegetables and meats. Unfortunately, paraffin has the
disadvantage of being readily softened by moderately elevated
temperatures. Also, while paraffin coating can sometimes enhance the
compressive strength of the fiberboard and resistance to puncturing, the
enhancement may not be sufficient for many uses. In view of the
shortcomings of reinforcing fiberboard using paraffin, other polymeric
resins, particularly various thermoset materials, have been considered for
this purpose. Many cured thermosets have the advantage of being very
rigid. As a result, fiberboards reinforced with cured thermosets tend to
have high resistance to compression. Unfortunately, many currently favored
thermosets are extremely brittle after being fully cured and fracture when
subsequently creased or folded. Such fracturing of the thermoset
reinforcing agent can readily extend to the fiberboard itself, thereby
seriously reducing the integrity of the container made therefrom along
edges and at corners.
Phenolics have received the greatest attention, particularly as a
reinforcing agent for corrugated paperboard. Representative U.S. Pat. Nos.
disclosing use of phenolics include U.S. Pat. Nos. 3,886,019, 4,096,935,
4,051,277, and 4,096,305 to Wilkenson et al. These patents disclose the
application of thin films of phenolic resin to surfaces of linerboards and
corrugated medium that will be adhered together to form the corrugated
paperboard. After adhering together the linerboards and corrugated medium,
the corrugated paperboard can be cut, scored, and slotted to make box
blanks. Because of the brittleness of the fully cured treated board, full
curing of the resin is delayed until after the box blanks have been folded
to make cartons.
Various thermoset blends of phenolics with other resins have also been
tried in an attempt to reduce the brittleness of phenolic alone.
Representative U.S. patents include Reisman et al U.S. Pat. Nos. 3,687,767
(phenolaldehyde), LeBlanc et al. U.S. Pat. No. 3,607,598 (phenol-aldehyde
plus polyvinylalcohol), Reisman U.S. Pat. No. 3,616,163 (phenolaldehyde
resole), Elmer U.S. Pat. No. 3,619,341 (phenol-aldehyde resole), Burke
U.S. Pat. No. 3,619,342 (phenol-aldehyde resole), Reisman et al. U.S. Pat.
No. 3,697,365 (resole phenolic plus an organosilyl compound), LeBlanc U.S.
Pat. No. 3,682,762 (resole phenolic plus polyaminoalkyl substituted
organosiloxane), LeBlanc U.S. Pat. No. 3,617,427 (aminoplast-modified
phenol-aldehyde resole), Carlson U.S. Pat. No. 3,617,428 (aminoplast with
phenol-aldehyde resole), and LeBlanc U.S. Pat. No. 3,617,429 (aminoplast
plus phenol-aldehyde and polyvinylalcohol).
Despite these developments, even phenolic blends tend to be unacceptably
brittle, which imposes certain limitations on manufacturing processes. For
example, in all the phenolic-blend patents recited above, curing
(thermosetting) of the resin is performed only after corrugating the
medium fiberboard or even later such as after the corrugated paperboard is
scored along fold lines. This means, for example, that resin-coated
paperboard destined to become the corrugated medium cannot be cured before
it is passed through a corrugating machine. As a result, conventional
thermoset-impregnated medium paperboard cannot be made up and cured in one
location and supplied to another location for corrugating and
incorporation into corrugated paperboard using conventional machinery.
Also, interposition of resin-applying and resin-curing machinery into
existing production lines for manufacturing corrugated paperboard is
expensive. These and other problems with existing methods can result in
prohibitively high production and shipping costs.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a polyether-reinforced
fiber-based material is provided which comprises, at least, a single ply
of a fibrous material impregnated with polyether on at least one of the
faces (i.e., major surfaces) of the ply. Each such impregnation, termed
herein a "polyether-impregnated stratum of fibers," extends depthwise from
the corresponding face into the thickness dimension of the ply no greater
than about one-half the thickness dimension. That is, the ply of fibrous
material can have a polyether-impregnated stratum on either or both faces.
However, whether a stratum is located on either or on both faces, a
portion of the thickness dimension is left unimpregnated with polyether.
Therefore, if such a stratum is located on both faces, each stratum has a
thickness dimension preferably no greater than about one-third the
thickness dimension of the ply.
Each polyether-impregnated stratum of fibers results in part from the
application of a liquid resin mixture to the corresponding face of the
ply. The resin mixture comprises an epoxy resin (resin "A") and a
hardening agent (resin "B"). Unlike conventional epoxy resin mixtures, the
"resin mixture" used according to the present invention has a watery
consistency as a result of the "epoxy" molecules of resin "A" being in a
substantially non-prepolymerized form.
Although the fibers comprising the ply can be any of a wide variety of
fibers, including hydrophilic and hydrophobic fibers, they are preferably
wood pulp fibers. The fibers are preferably organized into a sheetlike web
having a porosity sufficient to absorb a liquid epoxy resin mixture
applied to the web for the purpose of forming a polyether-impregnated
stratum. Most preferably, the wood pulp fibers are in the form of a
paperboard.
Polyether-reinforced fiber-based materials according to the present
invention exhibit high ring-crush strengths at low loading levels of
polyether. For example, a polyether-reinforced paperboard according to the
present invention contains a loading level of polyether of about 5% w/w or
less, yet exhibits a ring-crush strength greater than ring-crush strengths
of other polymer-reinforced materials, such as phenolic-reinforced
materials, having loading levels of polymer at least twice as high.
It has been unexpectedly discovered that the foldability of
polyether-reinforced fibrous materials according to the present invention
is excellent. All the reasons for such excellent foldability are not
understood at this time. One important contributing factor is that the
resin mixture applied to the fibrous material according to the present
invention is in a "substantially non-prepolymerized" form. As it cures,
the molecules comprising resin "A" undergo less extensive crosslinking
than conventional "epoxies," thereby producing a polyether that has much
less brittleness than polyethers produced using conventional epoxies.
Leaving a portion of the thickness dimension unimpregnated with polyether
also contributes in part to the ability of the polyether-reinforced
material according to the present invention, despite the fact that the
polyether is fully "cured," to be folded and creased without fracturing.
This is in contrast to analogous prior-art materials that are generally so
brittle that folding, and especially creasing, will cause fracture of the
material along the fold line. In fact, certain polyether-reinforced
fibrous materials according to the present invention have exhibited
foldabilities that are substantially no less than the foldabilities of
corresponding fibrous materials without any polyether reinforcement. At a
given ring-crush strength, the foldabilities of polyether-reinforced,
fiber-based materials according to the present invention are much higher
than the foldabilities of prior-art materials having equal ring-crush
strengths.
According to another aspect of the present invention, the
polyether-reinforced fiber-based material can comprise multiple web plies
superposedly adhered together, wherein at least one of the faces of at
least one of the plies has a polyether-impregnated stratum. Hence, the
present invention encompasses polyether-reinforced "corrugated paperboard"
comprising at least one "linerboard" and at least one "corrugated medium
paperboard," wherein at least one of said plies has at least one
polyether-impregnated stratum. Preferably, but not necessarily, the
corrugated medium contains one or more of the polyether-impregnated
strata. Such corrugated paperboard can also be comprised of more than one
corrugated medium, each sandwiched between and adhered to coextensive
linerboards.
The crush resistance and foldability of materials according to the present
invention permit the materials to be prepared at one location, including
full curing, and used at a different location. For example, it is possible
to manufacture polyether-impregnated medium paperboard at one plant and
ship the paperboard to a second plant at which the paperboard is
corrugated for making into corrugated paperboard. It is also possible for
fully cured polyether-reinforced corrugated paperboard according to the
present invention to be made at one location, then cut, scored, and folded
to make cartons at another location. In other words, the end-user of the
material does not have to be concerned with curing the material, in
contrast to end-users of analogous prior-art materials.
As another aspect of the present invention, methods are provided for
manufacturing such polyether-reinforced fiber-based materials. In a
representative embodiment, an epoxy resin mixture is applied to one or
both faces of a fibrous web at a loading level that ensures that the resin
mixture does not penetrate into the thickness dimension of the web more
than about half the thickness dimension (if applied to only one face) or
about one-third the thickness dimension (if applied to both faces). Hence,
the maximal loading level (the magnitude of which will, of course, depend
upon the particular nature of the web) is dictated by the necessity to
leave a portion of the thickness dimension of the web unimpregnated with
the resin mixture. Although heat and pressure are not required to cure the
resin mixture, curing preferably occurs by application of heat and
pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 comprises plots of ring-crush strengths of polyether-reinforced
paperboards according to the present invention as a function of the amount
of "hardener" (crosslinker) added to the resin mixture applied to the
paperboards.
FIG. 2 shows plots of ring-crush strengths and foldabilities of prior-art
polyether-reinforced paperboards as a function of loading level.
DETAILED DESCRIPTION
In a method according to the present invention, a liquid epoxy resin
mixture is controllably applied to either the obverse face or the reverse
face, or both faces, of a porous, sheetlike fibrous web. The resin mixture
is subsequently cured to transform each epoxy-impregnated face into a
polyether-impregnated stratum. Each polyether-impregnated stratum does not
extend through the thickness dimension of the web. In other words, even if
the web possesses a polyether-impregnated stratum on both faces, the web
still retains a non-impregnated stratum within the thickness dimension of
the web.
As referred to herein, a "porous, sheetlike fibrous web" can comprise woven
or nonwoven fibers. Consistent with a sheetlike conformation, such a web
has a length dimension, a width dimension, an obverse face, a reverse face
parallel to the obverse face, and a thickness dimension extending between
the obverse and reverse faces. As is typical with fibrous webs, the
thickness dimension is porous.
Representative fibers, not intended to be limiting, comprising the web are
hydrophilic fibers such as cellulosic fibers (e.g., cotton, wood pulp,
rayon), carbohydrate fibers, polyvinyl alcohol fibers, substituted
cellulosic fibers, glass fibers, mineral fibers, proteinaceous fibers
(e.g., silk); and hydrophobic fibers such as sized wood pulp, cotton, or
rayon fibers, polyethylene fibers, polypropylene fibers, polyester fibers,
nylon fibers, polyvinylacetate fibers, treated glass fibers, and aramid
fibers; and mixtures of these fibers. If the fibers are synthetic
polymeric fibers, the fibers can be spun-bonded or heat-bonded.
A "polyether-reinforced fiberboard" is a product according to the present
invention made from a sheetlike web of fibers. When the sheetlike web used
to make the fiberboard is comprised substantially of wood pulp fibers, the
product is referred to as a "polyether-reinforced paperboard."
By way of example and not intended to be limiting, representative basis
weights of webs comprising wood pulp fibers (i.e., "paperboards") range
from about 10 to about 90 pounds per thousand square feet. It will be
appreciated that, since different fiber materials have different specific
gravity values and since webs made from different fiber materials may have
different densities, suitable basis weight ranges for other types of
fibers may be different from the stated range for wood pulp fibers.
A "resin mixture" as used herein is a liquid formulation comprising a
mixture of a resin "A" and a resin "B." Resin "A" is an epoxy resin
comprising molecules having an aliphatic (straight or branched),
alicyclic, aromatic, or aliphatic-aromatic core group. The molecules have
at least one terminal glycidyl
##STR1##
group. A wide range of such compounds are known in the art. Examples, not
intended to be limiting, include glycidyl esters; glycidyl ethers such as
butyl glycidyl ether and 2-ethylhexyl-glycidyl ether; diglycidyl esters;
and diglycidyl ethers such as 1,4-butanediol-diglycidyl ether and
bis-phenol A-diglycidyl ether. Resin "A" can comprise a mixture of these
various glycidyl compounds.
Resin "A," unlike the "resin" component of, for example, a conventional
epoxy "cement," is substantially non-prepolymerized. That is, the glycidyl
compounds comprising resin "A" exist predominantly as monomers and short
oligomers, such as dimers and trimers, rather than longer polymeric forms
typical of conventional epoxy cements. As a result, resin "A" has a watery
viscosity in contrast to the syrupy consistency of epoxy "cement" resins.
Resin "B," which also has a watery consistency, comprises a "hardening" or
"curing" agent for resin "A." Resin "B" can be any of a wide variety of
such agents known in the art for curing ("thermosetting") epoxies.
Representative curing agents, not intended to be limiting, include
polyamines, polyimines, phenols, carboxylic acids and anhydrides,
mercaptans, and cationic photo-initiators such as diaryliodonium salts and
triarylsulfonium salts. Resin "B" can comprise a mixture of various epoxy
thermosetting compounds. Preferably, polyamines such as diethylenetriamine
("DETA") or triethylenetetramine ("TETA") are used.
The resin mixture is prepared by combining resin "A" with resin "B" to
yield a substantially homogeneous mixture thereof. Whereas virtually any
amount of resin "B" can be added to resin "A," the best structural
properties are obtained when the amount of resin "B" in the mixture is no
greater than the amount of resin "A" in the mixture. After combining resin
"A" with resin "B," any of various known agitating or mixing means can be
employed to create a substantially homogeneous mixture of the resins.
Resins "A" and "B" can also be combined together into a substantially
homogeneous mixture by any of the various known continuous processes
adapted for this purpose.
Mixtures of resins "A" and "B" have a watery consistency when prepared.
That is, such mixtures have a viscosity typically less than 500 centipoise
and preferably 200 centipoise or less.
The resin mixture is preferably applied in a neat (undiluted) form to the
web. Since the resin mixture is watery, it penetrates readily into
virtually any porous fibrous material. However, a diluent miscible with
the resin mixture can be added thereto if required to facilitate
penetration of the resin into unusually dense fibrous webs. Any organic
liquid that is non-reactive with epoxies can be used as a diluent.
Preferably, the diluent is a low molecular weight monoepoxide such as a
monoglycidyl ether or monoglycidyl ester, such as glycidyl butanoate.
Other suitable diluents include, but are not limited to, propylene
carbonate and phthalate esters. If used, the amount of diluent is
generally within a range of about 5 to 20% w/w, relative to the mass of
the epoxy resin. As a diluent, propylene carbonate has certain beneficial
characteristics including substantially odorless, colorless, low
viscosity, low toxicity, low vapor pressure at room temperature, and low
flammability (boiling point: 242.degree. C.; flashpoint: 132.degree. C.).
Each polyether-impregnated stratum typically extends the length and width
dimensions of the web parallel to the obverse and reverse faces of the
web. When a polyether-impregnated stratum is located on only one face of
the web, the impregnated stratum preferably has a thickness dimension no
greater than about half the web thickness dimension and preferably between
one-third and one-half the web thickness dimension. When a
polyether-impregnated stratum is located on both faces of the web, the
strata each have a thickness dimension no greater than about one-third the
web thickness dimension. In either case, a portion of the thickness
dimension of the web is left unimpregnated with polyether.
Although fully impregnating the thickness dimension of the web may yield a
fiber-based material having even greater crush resistance, leaving at
least a portion of the thickness dimension of the web without any
polyether, according to the present invention, provides a unique
combination of crush strength and flexibility. Accordingly, if too much of
the thickness dimension is impregnated with polyether, the foldability of
the fiber-based material may be less than desirable for certain uses. If
too little of the thickness dimension is impregnated, the material may
exhibit insufficient crush resistance for certain uses.
As the resin mixture is applied to the web, it absorbs rapidly into the
pores of the thickness dimension of the web. The depth of absorption is
controlled by precisely controlling the "loading" of the resin mixture on
the surface of the web. As used herein, "loading" and "loading level"
refer to the mass of resin mixture (or the mass of polyether, after the
epoxy resin is cured) applied to a face of the web, relative to the mass
of the web. Of course, a particular loading level of resin mixture will
penetrate to different depths in the thickness dimensions of different
webs, including webs made of different fibers. Hence, different webs can
accommodate different loading levels before the requisite penetration
limits are exceeded. By way of example, not intended to be limiting, most
paperboards can be loaded with up to about 20% w/w resin mixture without
the resin excessively penetrating the thickness dimension of the
paperboard. Preferably, paperboards are loaded with 10% w/w resin mixture
or less for maximal economy. For any type of web, simple cross-sectional
examination of the thickness dimension of an impregnated web using a
microscope or other suitable examination instrument will enable one to
readily determine the particular loading level that will produce a
particular depth of penetration of the resin.
It will be appreciated that controlling the loading level involves applying
the resin mixture in a manner whereby the mass of resin mixture applied
per unit area of the web is precisely controlled. The resin mixture can be
applied to the web by any of various liquid-application methods including,
but not limited to, gravure printing, roller coating, and spraying using
apparatuses having one or a plurality of spraying orifices. A preferred
application method is gravure printing because it has been found that this
method provides precise control of resin loading on the web surface.
It will also be appreciated that polyether-reinforced webs according to the
present invention can be prepared by either a batch process or a
continuous process. Since various apparatuses capable of performing either
process are well known in the art, they will not be described further
herein.
"Curing" (or "hardening" or "thermosetting") an epoxy resin converts the
molecules therein to a polyether which is a type of thermoset material.
Curing of the resin mixture used according to the present invention occurs
via crosslinking reactions of the glycidyl moieties in resin "A" with the
molecules of hardening agent comprising resin "B."
Curing can occur at room temperature, but the time required (for self-cure)
may be inconveniently long. One way to increase the rate of curing is to
increase temperature and/or pressure. However, the curing temperature must
not be so high that damage to the resin mixture, polyether, or web
results. A general range for curing temperature is room temperature
(25.degree. C.) up to about 200.degree. C. A general range for curing
pressure is zero up to about 1000 psig. With paperboards to which the
resin mixture has been applied, curing is preferably conducted at about
150.degree. C. and about 800 psig for a time from about four seconds to
about five minutes. The preferred curing time at 150.degree. C. and 800
psig is about 5 minutes. Of course, since elevated temperature and
pressure increase the rates of the curing reactions, the higher the
temperature and/or pressure, the less time required to achieve the same
degree of cure.
Curing by application of heat and pressure offers the additional benefit of
compressing the web(s) during curing, which has been found to increase the
crush resistance of the polyether-reinforced material over the crush
resistance of similar material produced at the same loading level but
without application of heat and pressure. Nevertheless, curing without
compression tends to produce polyether-reinforced materials according to
the present invention that exhibit better fold resistance than materials
cured with compression. Fold resistance is also better with thinner
materials (since fold resistance is a measure of stiffness which is a
function of Young's modulus x thickness. Young's modulus increases with
increased compression, but does not increase proportionately with the
decrease in material thickness resulting from curing under compression.
Curing at elevated temperatures and pressures can be effected using any of
various devices known in the art for controllably applying heat and
pressure. Candidate curing devices include, but are not limited to, platen
presses and continuous belt presses. If necessary or desired, curing can
be performed by a regimen that includes two or more short applications of
pressure rather than a continuous application for the entire time required
to achieve full cure.
A polyether-reinforced fiber-based material according to the present
invention comprises at least one fibrous sheetlike web. When the
polyether-reinforced fiber-based material is comprised of only one web or
"ply," the ply comprises at least one substantially continuous
polyether-impregnated stratum of fibers located within the thickness
dimension of the web. The impregnated stratum can be located on either the
obverse or reverse face of the web or on both faces.
A polyether-reinforced fiber-based material according to the present
invention can also be comprised of multiple plies. In such multiple-ply
materials, it is not necessary that all the plies have a
polyether-impregnated stratum. The present invention encompasses
multiple-ply materials wherein only one ply thereof has at least one
polyether-impregnated stratum. The present invention also encompasses
multiple-ply materials wherein multiple plies each have at least one
polyether-impregnated stratum. Each stratum need not have the same loading
level.
In multiple-ply materials according to the present invention, each ply can
be made from the same or a different fibrous web. The webs need not all
have the same basis weight, thickness, porosity, or texture.
When the polyether-reinforced fiber-based material is comprised of more
than one ply, the plies are typically superposedly adhered together.
Adhering the plies together can be achieved by adhering non-impregnated
faces to non-impregnated faces, non-impregnated faces to impregnated
faces, and impregnated faces to impregnated faces. The outermost faces of
such multiple-ply materials need not be polyether-impregnated faces.
One example, not intended to be limiting, of a multiple-ply material
according to the present invention is a corrugated paperboard wherein at
least one of the plies thereof has at least one polyether-impregnated
stratum. As used herein, a "corrugated paperboard" is a widely recognized
product comprising at least two plies of paperboard adhered together,
where at least one of said plies is corrugated in a manner known in the
art. The corrugated ply is generally referred to as the "medium"
paperboard. At least one of said plies is not corrugated and is used as a
facing sheet for the corrugated paperboard. Hence, the non-corrugated ply
is termed a "linerboard." Typical corrugated paperboards are comprised of
a corrugated medium sandwiched between two linerboards adhered to the
corrugated medium. The linerboard(s) of a corrugated paperboard often have
a larger basis weight than the corrugated medium. Any suitable adhesive
can be used to adhere the linerboards to the corrugated medium. A
corrugated paperboard can also comprise multiple plies of corrugated
medium separately interposed between plies of linerboards. Corrugated
paperboards are widely used for making cartons and the like.
Since curing can occur at moderate temperatures, curing of the resin
mixture applied to a paperboard could be performed according to the
present invention simultaneously with corrugation of the paperboard. This
is because conventional corrugators impart a certain amount of heat and
pressure to the paperboard as the paperboard passes through the
corrugator. Simultaneous curing and corrugation can be advantageous when
making polyether-impregnated corrugated medium according to the present
invention because conventional process machinery can be readily and
inexpensively adapted to include a gravure coater, sprayer, or the like
without the need to add a separate curing device. In such an instance, the
gravure coater, sprayer, or the like is added to the process machinery
upstream of the corrugator. As the paperboard to which the resin mixture
has been applied passes through the corrugator, the resin mixture may
undergo curing simultaneously with impression of corrugations into the
paperboard.
Curing can also occur at ambient temperatures. I.e., the resin mixture can
undergo a "self-cure." As a result, it is not necessary to cure the resin
mixture on-line after applying the resin mixture to the web. For example,
it is possible to apply the resin mixture to a paperboard, corrugate the
paperboard, then allow the resin mixture to self-cure off-line.
As can be appreciated from the foregoing, the polyether imparts a
substantial reinforcement to a fibrous web, enabling the
polyether-reinforced web to exhibit a crush-resistance strength that is
greater than the crush-resistance strength of a corresponding
non-reinforced web. Hence, with products made from a polyether-reinforced
web produced according to the present invention, lesser amounts of fibrous
web are required to obtain a crush resistance equal to the crush
resistance of similar products made from non-reinforced web, which can
yield considerable savings in cost and weight while adding other benefits
such as wet strength.
It has unexpectedly been found that fiber-based materials reinforced with
at least one polyether-impregnated stratum according to the present
invention have excellent fold resistances. In fact, in certain instances,
the fold resistance of a polyether-reinforced web according to the present
invention is as good as a non-reinforced web. Thus, the present invention
makes it possible to substantially increase the crush resistance of a
fiber-based material without adversely affecting the fold resistance of
the material. Furthermore, reinforcing a fiber-based material with
polyether according to the present invention yields greater flexibility at
a given crush strength than exhibited by prior-art reinforced fiber-based
materials.
A key benefit of greater flexibility at equal strength is that it is
possible for cartons and the like to be made from fully cured
polyether-reinforced corrugated paperboard produced according to the
present invention, including such operations as cutting and folding,
without the paperboard breaking along cut and fold lines.
Polyether-reinforced fiber-based materials according to the present
invention can be adhered together using conventional adhesives. In part,
this is because the polyether impregnant is not present through the entire
thickness dimension of the web, as described above. For example,
reinforced corrugated paperboards can be assembled from a corrugated
medium and at least one linerboard (wherein at least one of the medium and
linerboards are polyether-reinforced according to the present invention)
using conventional water-borne adhesives such as starch-based adhesives,
latex-based adhesives, or latex-starch adhesives to adhere nonimpregnated
surfaces together. Alternatively, if desired, conventional non-water-borne
adhesives can also be used on either non-impregnated or impregnated
surfaces. Such non-water-borne adhesives include, but are not limited to,
hot-melt adhesives, polyurethanes, isocyanates, epoxies, rubber-based
adhesives, various solvent-borne polymers, mastics, and silicones.
Additional benefits of polyether-reinforced fiber-based materials according
to the present invention include:
(a) Wet resistance: the materials retain crush resistance even when wet,
which is of considerable benefit when the materials are employed in making
shipping cartons.
(b) Resistance to fracture, even after being folded a number of times. Such
resistance is due in part to the unexpectedly superior flexibility of
polyether (prepared from a resin mixture containing a substantially
non-prepolymerized epoxy resin) as a reinforcing agent and in part to the
fact that the polyether impregnant does not extend entirely through the
thickness dimension of the web. Hence, the non-impregnated portion of the
web can serve as a hinge during folding, even after a lengthy series of
folds. As stated above, the improved folding resistance is obtained,
however, when resin "A" is not pre-polymerized. It has been found that
conventional "epoxy" reinforcing agents made with pre-polymerized resins
do not yield good fold resistance, as disclosed in co-pending U.S. patent
application Serial No. 07/770,587, incorporated herein by reference.
A polyether-reinforced fiber-based material according to the present
invention also has potential uses other than packaging and storage
containers including, but not limited to, various laminates, skins, and
facings for paneling, plywood, and other construction materials; wall
coverings; and analogous uses.
In order to further illustrate the invention, the following examples are
provided.
EXAMPLES 1-23
In these examples, the ring-crush strengths (edgewise compression
resistance) and foldabilities of paperboard materials treated according to
the present invention (i.e., containing a polyether-impregnated stratum)
were determined. Ring-crush strength is an accepted measure of the crush
resistance of sheetlike objects. The ring-crush tests were performed
according to the TAPPI T818-OM-87 standard test procedure.
Folding endurance tests were performed on strips 1/2 inch wide and 6 inches
long according to the TAPPI T511-OM-83 standard test procedure. Briefly,
the folding endurance test comprises holding one end of a test strip in a
stationary position and applying a one-kilogram weight to the other end.
While applying the weight, the length of the strip between the ends is
repeatedly flexed over a 270.degree. arc until the strip breaks. Data are
recorded as the number of flexes until break.
The paperboard selected for these tests was a 42-pound basis weight Kraft
linerboard. Separate sheets of the linerboard measuring 12 inches by 12
inches were treated individually on one face with a resin mixture
according to the present invention at a corresponding loading level as
listed in Table I. Ten sample strips were ring-crush and foldability
tested for each example; each datum in Table I represents a sample mean
where n=10.
TABLE I
__________________________________________________________________________
Resin Parts of
Resin
Parts of
Load
Ring Caliper
Example
"A" Resin "A"
"B" Resin "B"
% Crush (lbs)
Folds
(mil)
__________________________________________________________________________
1 Butyl glycidyl ether
99 DETA
1 5.2
112 2863
9.4
2 " 97 " 3 5 110 1598
9.6
3 " 90 " 10 7.2
117 2301
9.3
4 " 50 " 50 6 132 1564
9.3
5 2-ethylhexyl glycidyl ether
99 " 1 4.9
101 2725
9.2
6 " 97 " 3 4.8
103 2516
9.5
7 " 90 " 10 4.5
97 2772
9.2
8 " 50 " 50 6 110 2259
9.5
9 bis-phenol A diglycidyl ether
99 " 1 4.9
112 1648
9.8
10 " 97 " 3 5 108 2736
9.4
11 " 90 " 10 4.8
171 1229
9.3
12 " 50 " 50 4.9
152 1662
9.4
13 1,4-butanediol diglycidyl ether
99 " 1 4.8
135 2122
9.3
14 " 97 " 3 5.1
139 1846
9.5
15 " 90 " 10 5.2
155 1670
9.6
16 " 50 " 50 5.1
147 1724
9.3
17 49:34 bis-phenol A/1,4
83 " 3 5.6
126 1885
9.3
butanediol diglycidyl ethers
18 49:34 bis-phenol A/1,4
43 " 50 5.3
152 1383
9.8
butanediol diglycidyl ethers
19 25:18 bis-phenol A/1,4
83 " 3 5.6
119 1681
9.3
butanediol diglycidyl ethers
20 25:18 bis-phenol A/1,4
43 " 50 4.7
164 1937
9.7
butanediol diglycidyl ethers
21 bis-phenol A diglycidyl ether
97 TETA
3 4.9
102 2299
9.5
22 " 50 " 50 4.8
108 1547
9.6
23 untreated control
0 -- 0 -- 85 2204
9.7
__________________________________________________________________________
The resin mixtures were applied to the sheets using a gravure coater. The
resin mixture was cured by heating the treated sheets at 150.degree. C.,
800 psig for about 5 minutes.
After curing, the treated sheets were cut parallel to the machine direction
of the sheets into strips 1/2-inch wide and 6 inches long using a
precision cutter. For ring-crush testing of each example, representative
strips from each example were individually rolled end-to-end into a
cylinder and placed into a specimen holder manufactured by Sumitomo Corp.,
Chicago, Ill. The holder with the test "cylinder" was then mounted on the
lower platen of a conventional machine adapted for applying a compressive
force. A progressively increasing axially compressive force was applied by
the machine until the cylinder experienced compressive failure. The
compressive force in pounds was recorded at time of failure. All tests
were performed at 50% relative humidity. The experimental control
comprised similar compressive tests performed using the same but untreated
sheets.
Results of the ring-crush and fold-resistance tests are tabulated in Table
I. Ring-crush data are also plotted in FIG. 1, showing ring-crush at 50%
relative humidity as a function of percent amine crosslinker (i.e., resin
"B"; DETA or TETA in these tests) in the resin mixture applied to the
sheets.
Turning first to the ring-crush data, it can be seen (FIG. 1 and Table I)
that treating the paperboard sheets according to the present invention
yielded polyether-reinforced paperboard sheets exhibiting appreciably
greater ring-crush strengths than untreated controls (ring-crush data
typically varied 1-5% from sample means; loading levels were generally
about 5%). With both monoglycidyl and diglycidyl ethers, increasing the
amount of amine crosslinker in the resin generally resulted in greater
ring-crush strength. However, the largest percentage increases in
ring-crush strength over the experimental control occurred with amine
crosslinker contents up to about 10%. Above 10% amine crosslinker, further
increases in ring-crush strength were comparatively small; in fact,
increasing the DETA amine crosslinker content in the bis-phenol A and
1,4-butanediol diglycidyl ethers from 10% to 50% actually resulted in a
slight decrease in ring-crush strength. These results indicate that 10%
amine crosslinker (resin "B") in these resins may represent a practical
upper limit to the amount of resin "B" actually needed for excellent
ring-crush resistance, at least for polyether-reinforced paperboards. Of
course, since higher amounts of amine crosslinker also work well, the user
can modify the relative amount of resin "B" to resin "A" to achieve
maximal strength at least cost.
It was also noted that generally greater crush resistance was obtained when
resin "A" comprised a diglycidyl ether (Examples 9-22) rather than a
monoglycidyl ether (Examples 1-8). The exception was bis-phenol A
diglycidyl ether/TETA (examples 21-22), which yielded data similar to the
monoglycidyl-ether compositions. The reason for this is unclear, but may
be related to the use of TETA as a hardener in examples 21-22 rather than
DETA. DETA mixed with bis-phenol A diglycidyl ether (Examples 9-12)
yielded ring-crush values that were appreciably higher.
It should be kept in mind that, in contrast with conventional epoxy resins,
resin "A" as used according to the present invention is substantially
non-prepolymerized. That is, resin "A" is not comprised of oligomers.
Thus, large amounts of resin "B," up to about 50%, do not generally cause
a significant decline in crush-strength. Thus, a cured mixture of resins
"A" and "B," even mixtures containing 50T resin "B, " appear to have a
lower crosslink density than cured conventional epoxy resins.
Turning now to the foldability data (Table I), it was noticed that
individual data varied as much as 50% from the sample means. (Sample-mean
data are presented in the "Fold" column of Table I.) Because of the
variability of the data, the only general conclusion that can be drawn is
that reinforcing paperboard web with epoxy resin according to the present
invention did not significantly degrade the foldability of the material,
compared to the untreated controls.
Thus, when the fold-resistance and crush-resistance data are considered in
combination, the data of Examples 1-23 indicate that reinforcing
fiberboard webs with polyether according to the present invention yields
not only an appreciable increase in crush resistance of the web but also
no significant decrease in fold-resistance over untreated controls. Use of
a substantially non-prepolymerized resin "A" was important in achieving
these surprising results. Foldability data (FIG. 2) obtained with similar
webs treated with a bis-phenol A glycidyl epoxy resin that had been
prepolymerized indicated that foldability decreased precipitously to zero
even with only 3% loading. The ring-crush data of FIG. 2, however,
indicates that crush resistance was about the same, at about 5% loading
level, as the data shown in FIG. 1.
Table I also includes a column containing "Caliper mL" data which pertain
to measured thicknesses of the corresponding polyether-treated
paperboards. Each datum represents a sample mean where n=10. In view of
the fact that the untreated control (Example 23) had a mean thickness of
9.7 mils, it appears that a small amount of compaction (compression) in
the thickness dimension occurred with the polyether-treated samples
(Examples 1-22) .
Various polyether-treated paperboards from Examples 1-23 were also
investigated to determine how deeply the corresponding mixtures of resins
"A" and "B" penetrated into the thickness dimensions of the paperboards.
The penetration-depth values (expressed as a fraction of total thickness
of the treated web) were determined by cutting the treated webs after the
webs were cured and examining the cut edges using a light microscope. Data
are presented in Table II.
TABLE II
______________________________________
Pene-
Ex- Resin "A" Parts
Resin "B" Parts
tration
%
ample E1 E2 E3 E4 DETA TETA Depth Loading
______________________________________
3 90 10 1/3 7.2
4 50 50 1/2 6.0
7 90 10 1/4 4.5
8 50 50 1/4 6.0
11 90 10 1/4 4.8
12 50 50 <1/4 4.9
13 99 1 1/2 4.8
14 97 3 1/2 5.1
15 90 10 1/3 5.2
16 50 50 1/4 5.1
17 48.5 34 3 1/2 5.6
18 48.5 34 50 1/4 5.3
19 25 17.5 3 1/3 5.6
20 25 17.5 50 1/4 4.7
22 50 50 <1/4* 4.8
______________________________________
E1 = Butyl glycidyl ether
E2 = 2Ethylhexyl glycidyl ether
E3 = Diglycidyl ether of bisPhenol A
E4 = Diglycidyl ether of 1,4butanediol
DETA = Diethylenetriamine
TETA = Triethylenetetramine
*Thick layer of epoxy remained on surface
The data of Table II indicate that adding more hardener (resin "B") causes
the resulting mixture of resins "A" and "B" to penetrate a lesser distance
into the thickness dimension of the web at a given loading level. This may
be because a greater amount of hardener results in a more rapid rise in
viscosity of the applied mixture of resins such that the mixture rapidly
becomes too viscous after application to the fiberboard to readily
penetrate further into the web. Also, TETA appears to cause more rapid
curing than DETA. A comparison of examples 12 and 22 indicates that this
is so, particularly since a thick layer of epoxy remained on the surface
of the web in Example 22.
While the invention has been described in connection with preferred
embodiments and multiple examples, it will be understood that it is not
limited to those embodiments. On the contrary, it is intended to cover all
alternatives, modifications, and equivalents as may be included within the
spirit and scope of the following claims.
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